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    <title>Document</title>
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<script>
    // 题目2: 将一个字符串里的大小写字符反转一下
    // （小写的转大写，大写的转小写）
    function strConvert(str) {
        let arr = [];
        for (let i = 0; i < str.length; i++) {
            if (str[i] > "a" && str[i] < "z") {
                arr.push(str[i].toUpperCase());
            } else {
                arr.push(str[i].toLowerCase());
            }
        }
        return arr.join(""); //用""分割去掉逗号
    }
    console.log(strConvert("HelloWorld"));
</script>